Diabetes mellitus is the most common of endocrine disorders, and is characterized by inadequate insulin action. Diabetes mellitus has two principal variants, known as Type 1 diabetes and Type 2 diabetes. The latter is also referred to as DM/II (diabetes mellitus type 2), adult-onset diabetes, maturity-onset diabetes, or NIDDM (non-insulin dependent diabetes mellitus).
In the body, most carbohydrates are converted into glucose, which is then absorbed into the bloodstream. Therefore, eating carbohydrates usually makes blood sugar levels increase. As the glucose level increases in the blood, the pancreas releases an insulin hormone. Insulin is necessary to transfer glucose from the blood into the cells and use the glucose as an energy source in the cells.
However, in people with diabetes, the pancreas does not make enough insulin (Type 1 diabetes) or the body cannot respond normally to the released insulin (Type 2 diabetes). In both types of diabetes, glucose cannot absorb into the cells normally, thus causing a person's blood sugar level to increase excessively. Therefore, people with diabetes may keep track of their carbohydrate intake to be able to expect or predict increased levels of blood glucose when they have ingested foods containing carbohydrates.
Over the years, body characteristics have been determined by obtaining a sample of bodily fluid. For example, diabetics often test for blood glucose levels. Traditional blood glucose determinations have utilized a finger prick method using a lancet to withdraw a small blood sample. These systems are designed to provide data at discrete points but do not provide continuous data to show variations in the characteristic between testing times. These discrete measurements are capable of informing a patient the state of his blood glucose values at a point in time. Thus, the patient has enough information to administer “correction” amounts of insulin to reduce his current blood glucose reading. However, these discrete readings are not able to provide enough information for any type of automatic or semi-automatic system of administering insulin based on blood glucose values.
Recently, a variety of implantable electrochemical sensors have been developed for detecting and/or quantifying specific agents or compositions in a patient's blood or interstitial fluid. For instance, glucose sensors are being developed for use in obtaining an indication of blood glucose levels in a diabetic patient. These glucose sensors connected (wired or wirelessly) to a blood glucose monitor can provide continuous glucose readings over a period of time, such as 3 to 5 days. Such readings are useful in monitoring and/or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient.
Thus, blood glucose readings improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which are herein incorporated by reference. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated by reference herein. See also U.S. Pat. No. 5,299,571. In addition, characteristic glucose monitors used to provide continuous glucose data are described in commonly assigned U.S. patent application Ser. No. 11/322,568 entitled “Telemetered Characteristic Monitor System and Method of Using the Same” filed on Dec. 30, 2005, which is herein incorporated by reference in its entirety. In addition, infusion pumps receiving sensor data are described in commonly assigned U.S. patent application Ser. No. 10/867,529 entitled “System for Providing Blood Glucose Measurements to an Infusion Device” filed on Oct. 14, 2004, which is herein incorporated by reference in its entirety.
As sensor technology improves, there is greater desire to use the sensor values to control the infusion of drugs and medicine, such as insulin in a closed loop or semi-closed loop system. Specifically, a closed loop system for diabetes entails a glucose sensor and an insulin infusion pump attached to a patient, wherein the delivery of insulin is automatically administered by a controller of the infusion pump based on the sensor's glucose value readings. A semi-closed system typically includes a patient intervention step, wherein the amount of insulin to be infused as calculated by the controller of the infusion pump requires patient acceptance before delivery.
However, given the ramifications of over-delivery and/or under-delivery of medication, there has yet to be developed a working closed loop/semi-closed loop system that establishes sufficient safeguards for countering the over-delivery and/or under-delivery of insulin. In addition, there has yet to be developed a working closed loop/semi-closed loop system providing robust real-time calibration adjustment procedures which allows a patient to forgo calibration as needed.